Pull out one disc of pie dough and let it warm up a little and become pliable. This may take 20-40 minutes. Roll out the bottom crust. Press into the pie plate and trim the edge. Put it into the fridge to chill while you make the filling.
Give the peaches a good scrub. This will remove some of the fuzz. Finely dice one peach and set it aside. Then slice the remaining peaches into 1/2 inch thick wedges.
In a medium saucepan combine the diced peach with sugar, cornstarch, orange juice, bourbon, butter and salt. Bring to a boil, then lower the heat and simmer for 4-5 minutes, until the sauce is thick and the fruit is softened.
In a large bowl toss the sliced peaches with 1 tablespoon tapioca flour and vanilla. Add the cooked fruit and sauce. Toss everything together and let cool.
Take out the dough for top crust and let it warm up like before. For a lattice, roll the dough into an oblong. For a 5x5 lattice each 1 inch wide you will need a shape which is about 12x10 (so you have a little extra). If you want to do braids or stamps I would recommend making an extra portion of dough and roll that one out into another oblong.
Heat the oven to 425F. And place a baking sheet on a lower oven rack (to catch drips).
Stir the filling and add another tablespoon tapioca flour if it seems very juicy. Pour the filling into the bottom crust. Crisscross the lattice over the top and add any stamped shapes. Trim off the edges of the lattice and seal by pressing down with a fork all along the edge.
Mix together egg with 1 tablespoon of water. Brush the pastry with the egg wash, including under any stamps. Sprinkle the top with coarse sugar.
Bake for 20 minutes at 425F. Then reduce the heat to 375F and bake for 20-30 minutes more, or until the filling is bubbling and the crusted is browned. If the top is browning too much before the pie is done, cover the top with a foil shield.
Let pie cool on a rack for at least 4 hours, or refrigerated up to 1 day.